Various procedures directed to remedying spinal disorders require that the vertebra of the spine be stabilized. Such procedures include spinal fusion. Pedicle screws are installed in pedicles of vertebra of a spinal portion to be fused. The pedicle screws include sockets for receiving and fixating a rod which is used to interconnect the vertebra in fixed relation to one another to stabilize the vertebra while healing takes place effecting fusion of the vertebra. Other medical procedures exist which require the implantation of formable metallic parts such as repair of broken bones requiring stabilization during the healing process.
In the case of first and second level spinal fusions, rods are typically provided pre-bent to a desired curvature required to restore the natural curvature of the spine. In cases of multi-level fusions, such as the correction of spinal deformities, rods are provided straight and bent by surgeons in the operating room to be custom configured to the needs of the patient. The bending is done manually using instruments such as a French bender or in-situ bending devices. The rods used are formed of stiff materials with high yield stress such as titanium alloys. For example, Ti-6A1-4V titanium has a yield stress of 110,000 psi. Hence, force applied to such material exceed the yield stress to effect permanent deformation of the material. Bending rods is a difficult procedure which is complicated by work hardening of the rods due to bending and elastic strain of the material which results in spring-back.
A bending machine for use in operating rooms has been proposed and implemented. See Richard Ryan Pilson, Automated Manufacture of Spinal Instrumentation (Feb. 6, 2006) (unpublished MSME thesis, Virginia Polytechnique Institute & State University) (on file with Virginia Tech's Electronic Theses and Dissertations http://scholar.lib.vt.edu/theses/available/etd-02192006-214714/) which is herein incorporated by reference. The bending machine incorporates feedback affected by a digital encoder which measures deflection both with bending pressure applied and after bending pressure is removed to determine spring back and subsequent bending angles to achieve a desired bend. Such a system measures one bend at a time by deflection of a feeler apparatus which makes contact with the rod to be bent and deflects with the rod to rotate a digital encoder which in turn provides a measurement of the deflection of the rod. Rods requiring multiple bends are formed with each bend being measured and data stored (local bend) so that a final rod shape may be determined by mathematically adding measured deflections along the rod to determine a final rod shape (global bend). This system is prone to cumulative errors in the successive bending process and does not provide a real-time measurement of the final rod contour as only one bend at a time can be measured. Hence, verification of the actual final contour of the rod cannot be made. The present disclosure describes an improvement over these prior art technologies.